Wiring Ejection Charges

AZWoody wrote:


I've heard this same story several times. I believe the current NAR policy encourages people to join Tripoli just to get their L3. I have nothing against TRA but as a NAR member and Section Advisor it bothers me when NAR members feel that their organization is not serving them.
I've been trying for the past two years to get the NAR to *consider* a change to this requirement. Every example that I've been given regarding unintended discharge of the ejection charges could have been avoided by following a strict checklist. For example, if you fly the G-Wiz for your L3 you better know about the reversed polarity problem (and it better be documented in your package). There should be a ground test *before* BP is introduced to make sure the altimeters power up properly and go through their self-check (this is what I do). In the case of the G-Wiz there should be very clear visual clues to the proper polarity to hook up the battery and it should be verified (as part of the checklist) before flight.
I believe that it is more important for the L3 candidate to learn and demonstrate proper safety *procedures* than it is to know how to wire up a multi-pole switch (FWIW I used a 4PDT switch for my L3, one per altimeter, so yes I know about both procedures and multi-pole switches).
If you agree that this area of the NAR L3 program should be modified please contact the NAR L3CC chair, David Schaefer, and the NAR Board of Trustees. Ask for this to be discussed by the entire board, not just the Sports Committee or the L3CC, at the next BoT meeting.
Alex Mericas NAR L3
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Just out of curiousity, how does someone wire up a Gwiz backwards? Isn't the 9v battery pigtail soldered to the circuit board?
--
Tweak

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Tweak wrote:

The connector for the electronics is soldered in, but there is a jumper that allows you to power the pyro channel with a separate battery. You remove the jumper and attach the battery wires. If you get the polarity wrong the pyro channel will activate as soon as you power up the altimeter. This is documented in the instruction manual and, as I said, should be reflected in the L3 package. I always test my altimeter / ematches before adding BP. If the Discovery channel flight had done this it would have fired the pyro channels during bench test before powder was present. Might require a change of undies but not much more.
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Alex Mericas wrote:

You have it backwards, at least for the LC series. The soldered in 9V battery clip powers both the altimeter and the pyro outputs. If you want a separate battery you remove a jumper and connect another battery which powers the altimeter. The hard wired battery connector now powers the pyro channels only.
"To ‘split’ the pyro and computer power, remove the jumper between JP1 pin 5 and JP1 pin 7. The soldered-in battery wires now provide power to the pyro channels ONLY. The user must wire a second battery harness the JP1 pin 7 (+) and JP1 pin 8 (-)."
http://www.gwiz-partners.com/g-wiz_lc_users_manual_1_21.pdf
As I recall, the altimeter side does have a diode to protect the electronics from reversed power.
Of course you still have the problem of accidentally touching the clip to the battery backwards. Which is why a switch is still a very good idea.
--
David W. Schultz
http://home.earthlink.net/~david.schultz /
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David Schultz wrote:

Opps. You're right, I was doing it from memory. But still, this is well documented and any L3 candidate using such a device had better include procedures for avoiding this well documented design, er, feature. Back when I had a Gwiz I added an on/off switch to the altimeter power. A ground test in this configuration, without BP, would show polarity problems immediately.
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Alex Mericas wrote:

There is not now nor has there ever been a "shunt" rule for NAR L3 certification!
I believe that the current requirement is a good thing. It compensates for many altimeters not having any sort of safe/arm provisions at all.
You are unlikely in the extreme of modifying the L3 requirement as it is now included in the newly revised NAR safety code for _all_ high power rockets:
"If my rocket has onboard ignition systems for motors or recovery devices, these will have safety interlocks that interrupt the current path until the rocket is at the launch pad."
--
David W. Schultz
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David Schultz wrote:

This was discussed AT LENGTH on the NAR sections list and the conclusion was that this is NOT the same as the L3 requirement. An on/off switch for the altimeter satisfies the safety code.
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Alex Mericas wrote:

OK, they aren't identical requirements. But as they are adding something to the safety code it seems unlikely to me that something would be removed from the L3 requirements.
--
David W. Schultz
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David Schultz wrote:

You may be right. But I'll keep pushing until the BoT votes on it and then I'll abide by their decision. Its a moot point for me since I already have my L3.
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Right from the NAR website (http://nar.org/pdf/L3certreq.pdf )
See section 2.3/2.4
This is above what 1127 requires.
I know the guy that got the "shunt" BS adopted by NAR. His level 3 looked like the control panel of the space shuttle (lots of switches, and many points of potential failure). Lubliner, then still a L2, but head of the LC33, said "cool.. Lot's of switches, so it looks safe" (paraphrase). "I'll make you part of the L3CC, as you really know safety!" (paraphrase). But the Space Shuttle commander did become part of the L3CC soon after. And BTW, is no longer part of the L3CC.
I was planning my L3 at the time and knew that I'd be expected to provide a control panel much like the ISS if I was to make it past Lubliner (still a L2) and the captain of the Space Shuttle. (with one l3 under his belt).
So I joined TRA. Had TAPS that are well known - Mark Clark and Robin Meridith (if you don't know them, you should know who AHPRA is, or atleast heard of BALLS).
The "shunts or opens" to the ematches add SQAUT to safety. Many think "safety ends at the flight line". But adding more points of potential failure does nothing for the guy on the ladder, arming stuff on the pad, as occurred at a recent LDRS. It also does nothing for a bird coming in ballistic, because one of the additional points for failure, failed...
Moot point, as I've had my L3 for some time now (since 2000). The real trouble isn't the process, but the merit badge system. Some people just want to get to L3 too fast, without really having the background knowledge. Yes, I've had a few bad flights on L1/ L2 motors, but the important thing was that I learned from my mistakes. That's why I took my own time to move between levels. I think many that have attended a launch of any size know what a "heads up" flight is. We used to have "Hard hat" flights, where a few of the experienced folks would don construction hardhats, when a questionable flier was about to fly a questionable bird. And the funny thing is that questionable flights included some by the guy got his L3 under Lubliner, and quickly became part of the L3CC.
I've seen far to many people that had never seen a reloadable more prior to the day they did their L1 (there are G and below reloads, after all), and come back a month later to do their L2, and then come back a few months later to do a L3.
Been a NAR section advisor, as well as a TRA prefect, and trust me, I could tell you all some stories.......
As far as the guy that questioned my background, all I can say is that I've RSO'd Gate Bros flights. I've been involved in multi M motor flights.
Can the same bee said for anyone on the NARBOT?
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David Schultz wrote:

And it results in people joining Tripoli just to get their L3.
Perhaps the Tripoli policy is the one that needs changing. Either way, they should be equivalent.
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Hi David,
someone quizzed the BOT on this paragraph on NAR sections group.
several said a power off system is fine for this requirement.
for example,
I have a rocket with four on-off switches (N3 screw ins) powering 4 such devices.
I will not be adding yet another four switches to add "extra" interrupts to the e-matches.
My on-off switches, "interrupts the current path to the igniter" till the rocket is on the launch pad.
Nothing in that safety code says power off is not enough, like the L3 specs have added to them by you know who. This got debated on the BOT section group and that was the censuses that is archived in that yahoo groups threads.
I test by the way, with no BP involved and once BP is added, nothing better be powered on again till that rocket is on the launch pad.
By the way David, I love your attention to the legal issues, you are always right on target, thank you for that service.
CD
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Not all altimiters shunt when they are off. In the past there have been problems with ematches blowing when people reversed polarity going into their electronics, power oscillation caused by twisating wires together instead of using a switch & bumping the rocket among others. Shunting is not a bad idea although I think most people don't do it.
I don't think I've ever heard of an ematch being set off by RF but, I have heard people mention the possibility many times.
Also, it sucks if you forget to remove the shunt before flight.
Phil
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Humm,, thinking on this one.
Shunting could damage the FET on an altimeter if not done right. then the altimeter will act like it works, but never fire the charge, resulting in a balistic recovery.
Almost all incidents I have seen of many charges going off wrong, shunts would not have helped.
They either would fire the charge when the shunt was pulled, or fried the altimeters FET and resulted in a ballistic recovery instead.
now we need to determine what's worse, a charge going off or a ballistic recovery ?
Cranny Dane
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wrote:

THe FET will not be damaged by shunting under NORMAL circumstances. IF the outputs of the FET are shunted AND it attempts to fire the charge they can be but they are not certain to be. So the potential FET damage may possibly occur under conditions where you are trying to prevent charges froom going off / trying to insure safety. Seems like worthwhile to me.
Phil
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http://www.irving.org/rocketry/igniters/summary.html was an attempt to study the issue.
AZWoody wrote:

--
Will Marchant, NAR 13356, Tripoli 10125 L3
snipped-for-privacy@amsat.org http://www.spaceflightsoftware.com/will /
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writes:

Nope. SPDT can break the firing circuit AND shunt the ematch. Note NO center off position for this application.
        <-------o---------------->             .     ematch        .            altimeter             .         <-------o . . .    o-------->
--
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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Larry,
I agree with AZWoody. Adding a switch or shunt to the ematch adds another failure point to the system. If you want a switch, add it where it will do the most good - to power your alt off and on. A voltage selector switch from a computer power supply is my favorite switch to use for that purpose.
--
Joe Michel
NAR 82797 L2
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J.A. Michel wrote:

Yes , the proper way to do this is to use a keyswitch (use a Jameco mini key switch) and place it on the negative/black wire line from the 9V battery. You throw the switch to test continuity when packing the rocket, the light goes on (I use GWiz) and the system is good to go. Switch it off, then carry it to the pad. Switch on just before leaving the pad and it's blastoff time.
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I just butted in on the conversation. This all sounds quite interesting. However, I don't know a thing about electronics. I would like to learn so I can start putting them in my rockets. Is there a book I can buy that is a good teacher for a beginer.
Thanks, KT
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